This invention relates to methods for manufacturing photoelectric conversion devices, and more particularly relates to methods including a step of eliminating short current paths resulting from the semiconductor preparing process.
Heretofore, a photoelectric conversion device which uses a non-single-crystalline semiconductor has been employed for solar cells of low retailing prices. Such devices have been produced mainly of compact types, for example with a small area such as several square centimeters whilst there have been some attempts to make a large area photoelectric conversion device such as of several thousands cm.sup.2 in order to lower the cost per unit area. The large area devices, however, necessarily have therein many imperfections such as pinholes and cracks, which constitute shorting paths or, at least, current leaking portions. The fill factor of the device is lowered very much due to the imperfections and thereby the photoelectric conversion efficiency is degraded very much. Because of this the devices are produced only at a small yield and the production cost is not reduced so much. It is desirable, therefore, to eliminate short circuit current paths from the device in production of such large area solar cells.
One example of such attempts to eliminate short circuits is disclosed in Japanese Patent Published Application No. 60-46080. This attempt utilizes an etching solution in which is dipped one surface of a semiconductor layer having a pin junction, the other surface being provided with an electrode which is applied with a voltage in a manner so as to etch short current paths selectively. One embodiment of the art is described in this publication, page 376, line 9 on the left column to the top line on the right column. The etching solution is a water solution of hydrogen chloride at 0.01 to 1 weight % and sodium chloride at 0.05 mol %.
There, however, are many shortcomings in the disclosed prior art. Namely, the etched portions must be selectively filled afterwards with insulating material. Also, a metallic film cannot be formed in advance of etching since the etching solution contains acid which dissolves metal. Further, the art requires an additional process to eliminate efficiently water or other impurities which contact the semiconductor during etching.
Also another measure has been proposed in U.S. Pat. No. 4,166,918. In that patent the effects of electrical shorts are removed by applying a reverse bias voltage to burn out the short current paths in a semiconductor layer which is provided with a thick thermet film. However, after the removal, possible passages through the semiconductor layer remain which might constitute short current paths.